Abstract:
Forest resources contribute significantly to the Kenyan economy. However, due
to pressures exerted by the growing population, this scarce resource is seriously
endangered. In particular, the Kakamega Forest has experienced serious degradation in
the past, though some restoration efforts have also been put in place. In this research, we
utilise time series Landsat imagery to characterise the changes and capture the trends
in land cover changes. Three epochs are utilised, namely, 1986, 1995 and 2005.
Pre-processing involved georeferencing and radiometric corrections. As a first step the
time series imageries were evaluated via a threshold analysis distinguishing between
‘forest’ and ‘non-forest’. Subsequently, a supervised multispectral classification
was performed distinguishing various land cover classes. Ground truthing for the
historical imagery was done using aerial photographs, topographic maps and site
visits. Actual land cover verification was based on amateur photographs taken in 1999
from an aircraft, and ground observations in 2008. For classification the maximumlikelihood
decision
rule
was
applied
considering
bands
3,
4,
5,
7
plus
7/2
for
thematic
mapper
(TM)/enhanced thematic mapper plus (ETM+) imagery and 1, 2, 3 and 4
for Multi-spectral scanner (MSS) data, respectively. The classification results form
a solid basis for a consistent and detailed evaluation of forest history between 1986
and 2005. Analysis results presented include graphs and pie charts of change in land
cover class areas over time as well as such allowing for true change detection with
transitions between the different classes. In this study, maximum likelihood supervised
classification change detection techniques were applied to Landsat images acquired
in 1986, 1995 and 2005 respectively. To map land cover changes in kakamega forest,
a supervised classification was carried out on the six reflective bands for the three
images individually with the aid of ground truthing data. Changes among different
land cover classes were assessed. During the study period, a very severe land cover
change had taken place as a result of agricultural and settlement. These changes in
land cover led to vegetation degradation. The effects of restoration efforts are
also captured in the research findings.
